UBC Theses and Dissertations
An experimental study on air-blast atomization of viscoelastic liquids Li, Larry Kin Bong
Motivated by the need to improve transfer efficiencies in spray coating, an experimental investigation into viscoelastic atomization using pre-formulated substitute test liquids is presented. These model liquids allowed for the decoupling of two common rheological phenomena: extension-thickening and shear-thinning. By maintaining similar values of surface tension, density, and rate-independent shear viscosity in the test liquids, and independently varying the extensional viscosity, the effect of elasticity was isolated and shown to act against the breakup of a spray issuing from a plain-jet air-blast atomizer operating at high aerodynamic Weber numbers (~1000). Flash photography revealed the presence of large-scale filamentary structures at breakup, which delayed discrete droplet formation until farther downstream of the atomizer where relative air-liquid velocities were reduced. Consequently, liquid elasticity led to an increase in the mean droplet size. This was confirmed by shadowgraphy measurements. Moreover, the hindering influence of elasticity on atomization was also supported by Particle Image Velocimetry measurements, which indicated that the elastic droplets, owing to their greater inertia, were better able to maintain their initial momentum.
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